Evaluation of progressive inelastic deformation induced by a moving axial temperature front for a welded structure

Abstract

An evaluation of progressive inelastic deformation under moving thermal fronts for a Y-shaped welded cylindrical structure has been carried out by a structural test and inelastic analysis. The progressive inelastic deformation was evaluated according to the Japanese liquid metal reactor design code which accommodates evaluation procedures of thermal ratcheting dominated by secondary hoop membrane stresses with negligible primary stresses and was compared with the test results. In addition the influence of the residual stresses at the welded joint, derived according to the UK R6 procedure, on global thermal ratcheting deformation was evaluated. The maximum residual deformation after seven cycles of the thermal load was measured to be 3.1 mm while the inelastic analysis using a combined isotropic and kinematic model hardening was 2.6 mm. The evaluation results by the Japanese code showed that the strain limit due to a thermal ratcheting load was reached after 12.5 cycles while that of the structural test was 9.4 cycles. The contribution of the weld residual stresses at the Y-shaped welded joint, derived according to the UK R6 procedure, to the strain accumulation was estimated to be less than 0.1% both in the circumferential and axial directions, which shows that the effect of the weld residual stress on the ratcheting strain is wiped out quickly due to the applied loading cycle.